Molecule of the Day

As was mentioned in the comments to my entry on a refrigerant Monday, what we use has changed quite a bit over the years. If you don’t know how a fridge or AC works (they’re the exact same thing), here’s what happens: know how evaporation something makes things cooler (e.g., sweat?). Condensing something makes things hotter by the same principle. Refrigeration involves evaporating something and using the cold for what you want, then moving the vapor somewhere and compressing it (turning it into hot liquid) and dumping that heat somewhere else. Then you evaporate it again and get some more of that sweet cold stuff. And on and on it goes.

Then, we know something about a good refrigerant. It should evaporate easily, but absorb a lot of heat as it evaporates, so it cools well. There are also some ancillary concerns. It should dissolve oil, because the compressor is a motor, and it needs oil. Finally it shouldn’t be that toxic or reactive. Sulfur dioxide, an old-timey refrigerant, absorbs a lot of heat in evaporation and dissolves oil well, but it’s toxic and (somewhat) reactive. 70-80 years ago, SO2 was used in one of the earliest electric refrigerators.


It’s not used today because of toxicity concerns, but as was mentioned in the comments, home refrigerators are a lot different than car A/C – that charge of refrigerant usually doesn’t leak out.


  1. #1 _Arthur
    July 18, 2008

    According to the Museum of Retro Tech, there were attempts to make Carbon Disulphide “steam” engines, with CS2 as the working fluid.

    “There are lots of reasons why using carbon disulphide as a working fluid is not a good idea. As soon as you depart from water or air, you find yourself dealing with something that is expensive, explosive, poisonous, or all three.”

  2. #2 _Arthur
    July 19, 2008

    Oh, here is the correct entry, still from the Museum of Retrotech

    In 1904 Willsie built two solar/SO2 power plants. One was a 6-horsepower installation in St. Louis, Missouri, and the other a 15-horsepower system in Needles, California.

  3. #3 Uncle Al
    July 19, 2008

    Cut to the inevitable Enviro-whiner bottom line: Expensive, shoddy, deadly. “Shoddy” was the first recycled wool. How well did that work out?

    US Patent 3992424: heptakis(trifluoromethyl)iodine is the heaviest gas by far, MW = 609.95 (SF_6 is only MW = 146.06, UF_6 MW = 352.02). Best of all, I(CF3)_7 has no static molecular structure. As with methyl tert-butyl ether legislatively enforce its use at obscene expense, then ban it for being lethal, then prosecute environmental cleanup obscene expense. Feel smug about it all and call for further “sacrifices.”

    Demand obscenely expensive studies to find a heavier gas.

  4. #4 Brad
    July 20, 2008

    One of the first industrial refrigerants was actually ammonia, mostly in ice production. It has obvious toxicity concerns and is not very efficient, but some of its salts also have a nice proclivity for detonation.

  5. #5 KMSL
    July 20, 2008

    Ammonia either still is or was recently in use in gas-powered refrigerators… just don’t try to drill a hole in the tank to let it out like my one-time boss did…

  6. #6 Curtis
    September 25, 2011

    What refrigerant could I use to replace the sulfur dioxide? Can I get sulfur dioxide? I am tring to restore an old refrigerator whice has sulfur dioxide in it the compressor and everthing else seems to work but I do not know what the correct operating pressures should be, because I have never work with this type of refrigerant. The unit does not have any service ports so I will have to install some.I am a HAVC/R tech

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